This invention is in the field of electrochemical fabrication of nano and micro-sized structures, including metallic, semiconducting, and polymeric structures.
Due to the versatility of electrochemistry for plating and surface finishing of a wide range of materials, the principle of electrochemistry has recently been pursued and applied for the fabrication of various metallic nanostructures.
For example, electrochemical deposition has been used to deposit large arrays of nanostructures in nanoporous templates, such as porous alumina or irradiated polymeric membranes.(C. R. Martin, Science 266, 1961 (1994); M. E. Toimil Molares, V. Buschmann, D. Dobrev, R. Neumann, R. Scholz, I. U. Schuchert, and J. Vetter, Adv. Mater. (Weinheim, Ger.) 13, 62 (2001); M L. Tian, J. U. Wang, J. Kurtz, T. E. Mallouk, and M. H. W. Chan, Nano Lett. 3, 919 (2003)). This template-based deposition typically provides metal nanowires as small as 40 nm in diameter and a few micrometers in length (Tian et al., ibid.).
Most recently, templated electrochemical deposition of metal nanowires on step edges of graphite has also been demonstrated, which produces metal nanowires having diameters as small as 15 nm (M. P. Zach, K. H. Ng, and R. M. Penner, Science 290, 2120 (2000)).
In the traditional probe-based electrochemical deposition method, a sharp conductive probe and a substrate are submerged in an electrolyte plating bath, and the localized electric field applied between the probe and the substrate induces local deposition when the probe is brought very close to the substrate. (R. A. Said, Nanotechnology 15, 649 (2004); J. D. Madden and 1. W. Hunter, J. Microelectromech. Syst. 5, 24 (1996)). The method has shown great potential as a fast and inexpensive way of fabricating arbitrary-shaped, high aspect ratio 3-D microstructures (e.g., columns and helices) on a wide range of conductive and semiconductive substrates. However, structures produced by this method are usually porous and have feature sizes in the tens of micrometers (Said, ibid.) due to the limitation in producing and maintaining a sharp conductive probe and in confining the electric field down to nanoscale dimensions. In addition, electrolyte bath-based deposition is not suitable for devices in which exposure to ionic solution needs to be avoided.
Iwata et al. report a technique of local metal plating using a scanning shear force microscope with a micropipet probe filled with an electrolyte solution (F Iwata, Y. Sumiya, and A. Sasaki, Jpn. J. Appl. Phys., Part 2 43, 4482 (2004)). Both dots and lines were deposited along the surface of a substrate. The smallest dot width reported was 90 nm. The electrochemical deposition was carried out by applying a constant voltage for the modification time under open-loop current control, and the deposited structures are simple surface patterns with no controlled extension in height. Iwata is also listed as the inventor of Japanese Patent Publication No. 2005-349346, which relates to a method of depositing a micro-substance on a substrate. As described in the English abstract, the method involves a micropipet filled with a liquid containing a charged microsubstance and having an electrode inserted into its interior. An electric field is applied between the electrode and the substrate, resulting in the deposition of the microsubstance on the substrate surface due to the electric field induced physical diffusion of the microsubstance. In addition, Iwata is listed as the inventor of Japanese Patent Publication No. 2005-349487, which reports a fine processing method and device in which a voltage is applied between a working fluid and a workpiece using a combination of a scan type shear force microscope and a hollow probe.
Japanese Patent Publication No. JP9251979 reports a minute working device for supplying a local area on a minute solid surface with a fluid without damaging the solid surface.